The present invention relates to a borehole pipe side entry apparatus and method and more particularly pertains to a subassembly for coupling in a string of pipe to facilitate communication between the interior and exterior of the pipe string.
A common use for such a side entry apparatus involves providing wireline communication between the exterior and interior of a pipe string through a "packoff" to facilitate the use of electrically operated communication devices in a borehole drilling operation.
Wireline sealing apparatus for borehole drilling and workover operations include apparatus referred to as "packoff" units for sealingly engaging elements in communication with pressurized members. Such packoffs are often used in drilling apparatus where drilling mud is pumped under pressure down a drill stem to a mud motor which drives a drill bit. The mud motor drilling operation is particularly advantageous for a type of borehole construction referred to as controlled drilling wherein the drilling head is directionally controlled to drill both vertically and laterally. Similarly, various forms of packoffs have been found effective in facilitating certain aspects of controlled drilling.
Controlled drilling by its very definition generally requires directional survey information, since, in order to assure that the intended hole course and destination are achieved, it is necessary to know in which direction the hole is tending at any time. The bottom hole position with respect to the top hole position can be calculated from inclination and direction readings taken from a survey tool positioned in the borehole. Implementation of the survey tool normally requires the assembly of a packoff unit in the borehole apparatus.
Survey tools have been found to be useful for all forms of drilling, whether controlled or uncontrolled, since each form of drilling is greatly affected by forces which operate upon the drilling head and tend to randomly direct the course of the borehole away from that desired. Drilling variables such as hardness of formations, in particular, may cause the course to wander since the drill bit seeks the path of least resistance. Borehole courses are also affected by the reactive torque produced by a rotating drill bit, which torque operates upon the length of drill pipe and tends to produce a spiral hole. These forces continually affect the drilling operation and may cause deviations from the intended course of the borehole even when the drilling is theoretically controlled. It has thus been observed that surveying of the borehole in periodic increments during which the drilling is momentarily stopped and a survey package is lowered into the hole, is oftentimes inadequate for desired controlled drilling accuracy. Techniques have thus been developed for continuous monitoring of borehole construction facilitating "true control" in drilling.
In the past, drilling has been controlled either through "conventional" or "steering" procedures. Conventional directional drilling is generally a blind process in which a hole section is begun in a particular attitude, by the use of attitude deviation devices, and drilled for a time thereafter without knowledge of its instantaneous attitude. Steering, on the other hand, is a continuous process in which the attitude of the hole is continuously measured in order that course corrections may be made continuously rather than after a section of the hole has been drilled. Steering is most often a technique that is used in connection with the aforesaid mud motor drilling systems, in which the drill pipe remains stationary and the drill is rotated by a mud turbine, or moyno motor, operated by high pressure drilling mud supplied from the surface. Actual steering, or deflecting capability, is provided by a deflection tool known as a "bent sub," which is a substitute section of drill pipe formed with a bend therein and positioned at the lower end of the drill string near the drill bit. The primary determinant of the angle at which the drill bit addresses the formation is the degree of bend in the bent sub. In order to turn the hole, the entire drill string is merely rotated at the surface to point the bent sub in a different lateral direction.
There are several types of attitude indicating or steering tool instruments adapted for positioning in the borehole to provide directional information. These instruments include gyroscopic, inertial, magnetic, and gravitational types. The key to steering is communicating information from these tools to the surface, wherein the utilization of a packoff generally becomes necessary.
Attitude sensing devices operate generally in either a "drilling interrupt" or a "while drilling" mode. Generally speaking, only the devices employing electrical or magnetic sensing elements can be used in the "while drilling" mode because of the necessity of transmitting the data up the drill string to the surface. In some instances, the actual transmission from the steering tool is via acoustical transducers which alleviate cumbersome wirelines. However, in most instances where assured reliability and cost are factors for the surface to the downhole communication link, a wireline is preferable. Such wirelines interconnect steering tools inside the pressurized drill stem with instruments on the surface and outside the drill stem, necessitating a packoff at some point there between.
A conventional and commonly utilized prior art approach to steering through attitude sensing in the "while drilling" mode includes the communication wireline, wherein a cable is threaded through a packoff unit at the surface of the borehole near the end of the drill pipe and suspended through the center thereof. The wireline, in this manner, connects the steering tool and monitoring instruments at the surface. This approach, while reliable and effective in steering the drill bit to facilitate true "controlled" drilling, creates other serious procedural and mechanical problems which are directly related to the drilling operation. For example, a cable extending through the center of the drill pipe serves to complicate the requisite drilling hardware and the procedural aspect of adding additional sections of pipe which is inherently necessary as the borehole becomes deeper. Since the cable must be fed into the borehole through the drill stem from a cable reel, or drawworks, on the surface, that end of the wireline is not readily detachable. The only feasible way found to add additional drill pipe sections has been by pulling the steering tool and wireline back to the surface. This procedure requires a steering tool which may be readily locked and unlocked in position in the drill pipe. There is also the problem of sealing the area of interconnection where the wireline enters into the drill pipe, the drill pipe must be in sealed communication with the mud pump which forces mud into the hole under pressure for driving the mud motor and carrying off cuttings. Therefore, the wireline must enter the drill pipe through the aforesaid surface "packoff" which is expensive and further complicates the procedure of adding additional drill pipe.
The apparatus of the present invention is especially adapted for drilling with a steering system by providing for a wireline to be suspended along the outside of the drill stem and to enter and be secured therein through a side entry packoff somewhere in the drill string and oftentimes near the drilling head. In this manner, the present apparatus overcomes many of the disadvantages of the prior art by providing for a wireline communication link which enters the borehole through the upwardly moving mudflow which is egressing around the drill stem rather than through a surface packoff. It may be seen that the surface packoff is effectively replaced by a "downhole," side entry packoff, and the step of pulling the wireline and steering tool out of the hole to add additional drill stem may be eliminated. Since the outside wireline may still serve to connect the steering tool with the surface monitoring equipment, the apparatus of the present invention permits an effective "while drilling" steering mode without the major operational disadvantages generally associated therewith.
Two different methods are used for running a wireline through a side entry sub in controlled drilling operations involving a steering tool. One method involves positioning a side entry sub in the drill string near the mud motor. In this method, the wire line cable is run through the side entry sub and made up with the steering tool which in turn is then seated in the muleshoe sub for proper alignment with the bent sub. For this alignment technique, reference can be had to U.S. Pat. No. 3,718,194. The steering tool is then run into the hole as the drill string is made up and the wireline runs on the outside surface of the drill pipe. The advantage to this method is that the wireline is not pulled through the packoff and thus not subjected to wearing forces. However, it may be preferable to run the steering tool into the pipe from the surface. Thus, the second method involves placing the muleshoe sub in the drill string above the bent sub and then running the drill pipe string into the borehole for drilling. Then, when it is desired to "kick off" the hole or control the direction of drilling in a "while drilling" configuration, the steering tool is run in from the surface. This involves placing a side entry sub in a made up drill string at the surface when the drill and mud motor are at or near the bottom of the hole. The cable is passed through the side entry sub and the steering tool is then "made up" on the wireline. The tool is then pumped down the drill string by mud circulation through the pipe string until it seals in the muleshoe sub near the bottom end of the pipe string. This method thus requires running the wireline through the side entry sub to the full depth of the "kick off". In order to permit the cable to move through the side entry sub without excessive wear, the sealing arrangement must be accomplished after the steering tool is seated in the muleshoe. However, it is difficult with present side entry subs to carry out this second method of operation without causing excessive wear to the wireline cable.
Another application for the use of a pipe side entry apparatus pertains to the logging of a highly deviated borehole and in particular boreholes that approach a horizontal disposition with respect to the earth's surface. During drilling operations, various logging tools are run into the borehole to determine physical parameters of the formations being traversed. Typically, in such logging operations, the drill pipe is removed and the logging tool is lowered or dropped into the borehole on a wireline which provides an electrical conductor path to trasmit data being measured by the tool to the surface for recording. However, in boreholes deviated toward a horizontal disposition, gravity forces are not sufficient to permit lowering of the tool through the borehole. In such a situation, one method of logging the hole is to pump a logging tool through a drill pipe. An apparatus proposed for such a logging operation in rotary drilling operations is shown in U.S. Pat. No. 3,016,963 which describes a pump down logging device having a measuring wand passing through the eye of the drill bit. A recorder in the tool accumulates data which is retrieved to the surface when the pipe string is pulled. However, in directional drilling operations using a mud motor, the bottom of the drill pipe is closed for passage of a pump down logging tool of the type described above.
A means for effectively carrying out the logging operation described above with respect to highly deviated holes involves the use of a side entry sub much as in the manner described above relative to the second method of seating a directional drilling tool. In the logging operation, however, the motor and bit are not located in the pipe string and the lower end of the pipe string is open ended. Thus, the logging tool is capable of being pumped by mud circulation out the end of the drill pipe into open hole. Subsequently, the drill pipe string is raised, as sections of pipe are removed, and the logging tool is also raised while it is being operated to log the hole from the bottom up. This method of logging requires that the wireline be sufficiently packed off in the side entry to develop pumping pressure and at the same time, permit the wireline to pass through the side entry without excessive wear on the cable.
A prior art drill pipe side entry apparatus for use in drilling operations is shown in Base U.S. Pat. No. 4,062,551. The Base patent shows a side entry sub having a passageway for receiving a threaded plug. An opening in the plug receives the wireline cable and when the plug is secured in the passageway, a packing element below the plug is compressed to pack off the apparatus. One disadvantage of this device is that it does not provide for slipping the wireline through the apparatus in a logging operation. Also, it is not possible to assemble the device about the wireline after the wireline has been passed through the passageway in the sub. Tricon U.S. Pat. No. 4,200,297 shows a side entry packoff which has a wireline sealing member positioned in a passageway between a plug and an expansion member. By moving the expansion member toward the plug, the seal is compressed to seal the wireline in the passageway.
Van Wormer U.S. Pat. No. 2,355,342 shows apparatus for passing an electrical cable into a drill pipe through a sealed opening for operating a downhole electrical motor. This apparatus would be entirely ineffectual for the purposes of the present invention.
While these prior devices are generally concerned with the problem of providing a side entry communication between the interior and exterior of a drill pipe, they each offer disadvantages that do not permit an effective use of this concept, such as ineffective sealing, not permitting slippage of the wireline in certain applications, and most importantly, causing excessive wear to the wireline during the use of the side entry apparatus.
It is therefore an object of the present invention to provide a new and improved borehole pipe side entry apparatus for passing a tubular communications device from the exterior to the interior of a pipe string without causing excessive wear to the communications device, and at the same time, maintaining a pressure differential across the pipe string between its interior and exterior.